Clot retrieval device for removing clot from a blood vessel

ABSTRACT

A clot retrieval device  1  for removing occlusive clot from a blood vessel, the device comprises an inner elongate body  3  having a collapsed delivery configuration and an expanded deployed configuration and an outer elongate body  2  at least partially overlying the inner elongate body  2 . The outer elongate body  2  is expandable to a radial extent which is greater than the radial extent of the inner body  3  in the deployed configuration to define a clot reception space  11 . The outer elongate body  2  comprises a distal end portion  24,49  and the inner elongate body  3  comprises a main body portion  10  and a distal portion which extends in the deployed configuration towards the outer elongate body  2  to a greater extent than the main body portion. The distal portion  10  of the inner elongate member  3  and the distal end portion  24,49  of the outer elongate body  2  together define a three dimensional protective structure to substantially prevent distal egress of clot or clot fragments from the device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.14/629,217, filed Feb. 23, 2015, now U.S. Pat. No. 9,445,829 and issuedSep. 20, 2016, which is a continuation of International Application No.PCT/EP2014/054251, filed Mar. 5, 2014, which claims the benefit ofpriority of U.S. Provisional Application No. 61/785,213, filed Mar. 14,2013, each of which is incorporated herein by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to devices and methods of removing acuteblockages from blood vessels. The invention especially relates toremoving acute obstructions from blood vessels. Acute obstructions mayinclude clot, misplaced devices, migrated devices, large emboli and thelike. Thromboembolism occurs when part or all of a thrombus breaks awayfrom the blood vessel wall. This clot (now called an embolus) is thencarried in the direction of blood flow. An ischemic stroke may result ifthe clot lodges in the cerebral vasculature. A pulmonary embolism mayresult if the clot originates in the venous system or in the right sideof the heart and lodges in a pulmonary artery or branch thereof. Clotsmay also develop and block vessels locally without being released in theform of an embolus—this mechanism is common in the formation of coronaryblockages. The invention is particularly suited to removing clot fromcerebral arteries in patients suffering acute ischemic stroke (AIS),from pulmonary arteries in patients suffering from pulmonary embolism(PE), from coronary native or graft vessels in patients suffering frommyocardial infarction (MI), and from other peripheral arterial andvenous vessels in which clot is causing an occlusion.

BACKGROUND

There are significant challenges associated with designing clot removaldevices that can deliver high levels of performance:

There are a number of access challenges that make it difficult todeliver devices. In cases where access involves navigating the aorticarch (such as coronary or cerebral blockages) the configuration of thearch in some patients makes it difficult to position a guide catheter.These difficult arch configurations are classified as either type 2 ortype 3 aortic arches with type 3 arches presenting the most difficulty.The tortuosity challenge is even more severe in the arteries approachingthe brain. For example it is not unusual at the distal end of theinternal carotid artery that the device will have to navigate a vesselsegment with a 180° bend, a 90° bend and a 360° bend in quick successionover a few centimetres of vessel. In the case of pulmonary embolisms,access may be gained through the venous system and then through theright atrium and ventricle of the heart. The right ventricular outflowtract and pulmonary arteries are delicate vessels that can easily bedamaged by inflexible or high profile devices. For these reasons it isdesirable that the clot retrieval device be compatible with as lowprofile and flexible access and support catheters as possible.

The vasculature in the area in which the clot may be lodged is oftenfragile and delicate. For example neurovascular vessels are more fragilethan similarly sized vessels in other parts of the body and are in asoft tissue bed. Excessive tensile forces applied on these vessels couldresult in perforations and hemorrhage. Pulmonary vessels are larger thanthose of the cerebral vasculature, but are also delicate in nature,particularly those more distal vessels.

The clot may comprise any of a range of morphologies and consistencies.Long strands of softer clot material may tend to lodge at bifurcationsor trifurcations, resulting in multiple vessels being simultaneouslyoccluded over significant lengths. More mature and organized clotmaterial is likely to be less compressible than softer fresher clot, andunder the action of blood pressure it may distend the compliant vesselin which it is lodged. Furthermore the inventors have discovered thatthe properties of the clot may be significantly changed by the action ofthe devices interacting with it. In particular compression of blood clotcauses dehydration of the clot and results in a dramatic increase inboth clot stiffness and coefficient of friction.

The clots may not only range in shape and consistency, but also may varygreatly in length, even in any one given area of the anatomy. Forexample clots occluding the middle cerebral artery of an ischemic strokepatient may range from just a few millimeters to several centimeters inlength.

Stent-like clot retrievers are being increasingly used to remove clotfrom cerebral vessels of acute stroke patients. These are self expandingdevices, similar in appearance to a stent attached to the end of a longshaft, and are advanced through a microcatheter and deployed across clotobstructions in order to trap and retrieve them. They rely on a pinningmechanism to grab the clot by trapping the clot between theself-expanding stent-like body and the vessel wall. This approach has anumber of disadvantages:

A stent-like clot retriever relies on its outward radial force (RF) toretain its grip on the clot. If the RF is too low the stent-like clotretriever will lose its grip on the clot, but if the RF is too high thestent-like clot retriever may damage the vessel wall and may require toomuch force to withdraw. Therefore stent-like clot retrievers that havesufficient radial force to deal with all clot types may cause vesseltrauma and serious patient injury, and stent-like clot retrievers thathave appropriate radial force to remain atraumatic may not be able toeffectively handle all clot types.

The stent-like clot retriever pinning mechanism tends to compress thetrapped clot. This compressive force will tend to dehydrate the clot,which in turn tends to increase its coefficient of friction, making itmore difficult to remove from the vessel.

Conventional Stent-like clot retriever designs do not retain theirexpanded shape very well when placed in tension in bends, due to themanner in which their strut elements are connected to one another. Thiscan result in a loss of grip on a clot as the stent-like clot retrieveris withdrawn proximally around a bend in a tortuous vessel, with thepotential escape of the captured clot. This occurs because the struts ofthe stent-like clot retriever are placed in tension when it isretracted. This tension is due to friction between the device and theblood vessel, and is increased if an additional load is applied loadsuch as that provided by a clot. In a bend the struts on the outside ofthe bend are placed in higher tension than those on the inside. In orderto attain the lowest possible energy state the outside surface of thestent moves towards the inside surface of the bend, which reduces thetension in the struts, but also reduces the expanded diameter of thestent-like clot retriever.

Another disadvantage with this approach is that it relies on pinning theclot between the stent-like clot retriever and the vessel wall and thusmay not restrain the clot effectively when passing a branch vessel orwhen passing into a vessel that is larger than the fully expandeddiameter of the stent-like clot retriever.

Pinning the clot between the stent-like clot retriever and the vesselwall in order to remove it from the vessel also results in high shearforces against the side of the clot as it is removed, potentiallyreleasing fragments of the clot. If these fragments are not retained bythe device they may be released leading to further blockages in thedistal vasculature.

A particular difficulty encountered when attempting to remove long clotsis that conventional devices may be shorter than the clot itself. Adevice that is shorter than the clot is unlikely to be able to restoreflow through the occluded area upon deployment, and thus the pressuregradient across the clot remains a significant impediment to itsremoval. Simply making such a device longer would likely render itdifficult to track through tortuous anatomies and could be traumatic tothe vasculature, taking more force to withdraw and potentially gettingstuck and requiring surgery to remove.

For many reasons including some or all of the above limitations it isoften necessary for a physician to make multiple passes with a clotretrieval device in order to fully remove an obstructive clot. Howevereach time a clot retrieval device is withdrawn the access to the targetsite is lost. Thus it is necessary to re-advance a guidewire andmicrocatheter to access and re-cross the clot, and then remove theguidewire and advance the clot retrieval device through themicrocatheter. Navigating the guidewire and microcatheter to the clotcan take a considerable amount of time especially if the vessels aretortuous. This additional time and device manipulation all adds to therisks to which the patient is exposed.

The challenges described above need to be overcome for any device toprovide a high level of success in removing clot, restoring flow andfacilitating good patient outcomes. Existing devices do not adequatelyaddress these challenges.

STATEMENTS OF THE INVENTION

According to the invention there is provided a clot retrieval device forremoving occlusive clot from a blood vessel, the device comprising:—

-   -   an inner elongate body having a collapsed delivery configuration        and an expanded deployed configuration;    -   an outer elongate body at least partially overlying the inner        elongate body;    -   the outer elongate body being expandable to a radial extent        which is greater than the radial extent of the inner body in the        deployed configuration to define a clot reception space;    -   wherein the outer elongate body comprises a distal end portion;        and    -   wherein the inner elongate body comprises a main body portion        and a distal portion which extends in the deployed configuration        towards the outer elongate body to a greater extent than the        main body portion,    -   the distal portion of the inner elongate member and the distal        end portion of the outer elongate body together defining a three        dimensional protective structure to substantially prevent distal        egress of clot or clot fragments from the device.

In this aspect of the invention the embolization risk is reduced byproviding a distal net or scaffolding zone across the vessel lumentowards the distal end of the device. This scaffolding in this case isappended to both the inner or outer member or to both members, and isthree dimensional in that it has depth as well as surface area.Combining the scaffolding of both inner and outer members provides amore effective filter than utilizing one member alone. In some casesfibres or fine wires are utilised to provide added scaffolding withminimal impact on device profile or deliverability.

In one embodiment the distal portion of the inner elongate bodycomprises a plurality of struts which are configured in a volumetricpattern.

In one case the distal portion of the inner elongate body comprises abulged or flared framework of struts.

In one embodiment the distal end portion of the outer elongate bodycomprises distal struts. In one case the distal struts of the distal endportion of the outer elongate member are configured in a generallyconical shape.

In one embodiment at least some of the struts comprise an attachmentpoint, such as an eylet, for reception of a fibre. The protectivestructure may include a plurality of fibres providing a distal net.

In one embodiment the outer elongate body comprises a first monolithicstructure.

In one embodiment the inner elongate body comprises a second monolithicstructure.

In one case wherein the inner elongate body extends proximally of aproximal end of the outer elongate body.

In one embodiment the outer elongate body comprises a plurality of clotreceiving openings and a plurality of clot engaging regions, and whereinthe clot engaging regions are adapted, on engagement with clot, to urgeclot towards the clot receiving openings and into the reception spacebetween the outer elongate body and the inner elongate body.

The clot engaging regions of the outer elongate body comprisesscaffolding openings, the clot receiving openings being substantiallylarger than the scaffolding openings.

In one embodiment the outer elongate body comprises at least twolongitudinally spaced-apart segments. There may be at least one hinge isprovided between the segments.

The disclosed designs overcome many of the disadvantages of existingmechanical thrombectomy solutions.

Various interchangeable terms are used herein to describe those portionsof the invention that are configured to engage with the clot, beinggenerally deployed within the clot and engaging with it. These termsinclude “clot engaging portion”, “expandable member”, “expandable body”,“clot engaging element”; while the terms “elongate basket”, “engagingbasket” and “stent basket” may also be used to describe this portion ofthe device.

Designs are disclosed in which a clot engaging portion of the device isconfigured to be expanded within an occlusive clot in a blood vessel sothat the expanding engager allows the clot to migrate into a receptionspace within the body of the engager as the engager expands. The engageris delivered through a catheter to the site of the occlusion and ispositioned within the clot. The engager is expandable at the site of theocclusion and starts to compress the clot as it is expanded. The engagersurface comprises inlet openings and the inlet openings allow the clotto ‘escape’ from compression by displacing a significant portion of theclot through the inlet openings in the wall of the engager. Because asignificant portion of the clot is urged through the inlet openings inthe engager this minimizes compression of the clot and hence minimizesthe resultant increase in the clot coefficient of friction. This alsoreduces the radial force on the vessel in the region of the clot whichmeans a lesser force is required to withdraw the captured clot, which inturn means less vessel trauma and less tension on the distal vascularbed. The device is configured such that the radial force of the deviceacts strongly at a small diameter to engage with and grip clot, but actssoftly at a larger diameter to gently contact the vessel wall are alsodisclosed.

Designs with dual expandable members are disclosed whereby the devicecomprises a first inner expandable member and a second outer expandablemember the inner member being arranged substantially within the lumen ofthe outer member. The properties of the inner and outer members may betailored independently of each other. The inner member may have a verydifferent radial force to the outer member. The inner member may have avery different level of porosity to the outer member. The inner membermay have a fully expanded diameter that is very different to that of theouter member. The length of the inner member may be different to that ofthe outer member. The shape of the struts of the inner member may bedifferent to the shape of the struts of the outer member. There may be aclearance between the inner member and the outer member in the expandedconfiguration. There may be a clearance between the inner member and theouter member in the collapsed configuration. One, or both or neither ofthe inner and outer members may have a seam which runs substantiallylongitudinally along at least a portion of the wall of the member. One,or both of the inner and outer members may comprise a laser cut member,a braided member, a knitted member, an extruded member, a pultrudedmember, One or both of the inner and outer members may be manufacturedwith a process involving a laser cutting step, a braiding step, aknitting step, an extrusion step, a pultrusion step, an electropolishingstep, a heat treatment step. One or both of the inner and outer membersmay comprise a tapered section, a flared section, a closed end sectionor a closed mid section. One or both members may comprise asubstantially tubular or cylindrical section.

These dual expandable member devices have a number of benefits. (1) Theinner member can be configured to provide a strong opening force tocreate a lumen through the clot and restore flow immediately ondeployment. This flow lumen reduces the pressure gradient across theclot, making it easier to remove the clot. (2) The diameter to which theinner member expands may be tailored so as to reduce the risk of areperfusion injury. With this embodiment the inner member expands to adiameter that is significantly smaller than the diameter of the vesselimmediately adjacent to and distal of the occlusion. This small diameterinner member creates a small flow lumen across the occlusion andrestricts the initial blood flow to the affected portion of the brain.This restricted blood flow ensures that the pressure applied to bloodvessels immediately after flow restoration is lower than normal and thisreduces the risk of bleeding in the ischemic vascular bed. Fullperfusion is subsequently restored by removing the device and the clot.(3) The inner member may be configured to expand to a lesser diameterthan the outer basket and to a lesser diameter than any vessel in whichit is to be deployed. This means that a strong radial force may besafely exerted on the clot to open up a flow lumen, but need not beexerted on the vessel. (4) The inner member can serve to scaffold thelumen created through the clot, preventing the liberation of emboli fromthe clot into the resultant fast flowing bloodstream. (5) The innermember may at least partially comprise a stent and can provide a stronggrip on the clot for the critical initial step of disengaging the clotfrom the vessel, enabling the outer basket to be configured with a lowradial force. (6) The outer member may be configured to have large inletopenings so as to urge clot across the wall of the outer. The innermember on the other hand may be configured to prevent distal migrationor fragmentation or embolization of clot that traverses the wall of theouter member. By configuring the outer member so as to encourage clot totraverse the wall of the outer member the device can more effectivelydisengage clot from the wall of the vessel while the device is alsoeffective at preventing loss of clot material with an inner member witha shape and substructure that provides scaffolding.

Designs are also disclosed which further reduce this embolization riskby providing a distal net or scaffolding zone across the vessel lumentowards the distal end of the device. This scaffolding may be appendedto either the inner or outer member or to both members, and may be threedimensional in that it has depth as well as surface area. Combining thescaffolding of both inner and outer members may provide a more effectivefilter than utilizing one member alone. Designs are disclosed utilisingfibres or fine wires to provide added scaffolding with minimal impact ondevice profile or deliverability.

Designs are disclosed of devices with long and highly flexible innermembers which may extend significantly proximally of the outer member,enabling the device to be used to retrieve particularly long clots. Thesmall diameter and flexible inner member expands to provide a flow lumenthrough the clot (reducing the pressure gradient and making the cloteasier to remove) but does not expand to the diameter of the vessel inwhich it is deployed. Thus the resultant device can be delivered andretrieved more safely (at much lower forces) than a similar lengthdevice whose diameter was configured to engage with the vessel over itsentire length.

Designs are also disclosed of clot retrieval structures from whichportions can be detached and left in-situ as implants. This might bedesirable as a bail-out option in the event that the device becamelodged in place and the physician felt that the force required toretrieve device was too high to be safely applied. This might also bedesirable in the event that the occlusion was thrombotic oratherosclerotic—in which case the outer member could be detached andleft in place as a stent to maintain a flow lumen through the clot andscaffold the lesion. Detachable designs are disclosed in which the outermember can be detached from the inner member, and in which one or bothends of the outer member can be reconfigured to allow the outer memberto expand to a generally tubular shape which can appose the lesionand/or vessel wall.

Various embodiments of the invention are described in more detail below.Within these descriptions various terms for each portion of the devicesmay be interchangeably used as discussed previously. Each of thedescribed embodiments are followed by a list of further qualifications(preceded by the word “wherein”) to describe even more detailed versionsof the preceding headline embodiment. It is intended that any of thesequalifications may be combined with any of the headline embodiments, butto maintain clarity and conciseness not all of the possible permutationshave been listed.

In one embodiment of the invention the treatment apparatus comprises aclot retrieval device comprising:—an elongate member, and an expandableclot engaging element configured to extend across the clot in itsexpanded state, the expandable clot engaging element comprising a firstmonolithic structure and a second monolithic structure, the firstmonolithic structure encircling the second monolithic structure over atleast a portion of its length, the second monolithic structurecomprising a proximal section, an intermediate section and a distalsection, the distal section comprising an expansion.

Some optional features of this embodiment include:—

-   -   wherein the first monolithic structure is configured to        substantially encapsulate the second monolithic structure;    -   wherein the first monolithic structure comprises a proximal        section, an intermediate section and a distal section, the        distal section comprising an enclosed distal end;    -   wherein the distal end of the clot engaging element comprises an        enclosed distal end said enclosed distal end configured to        capture clot fragments and/or to prevent distal migration of        clot fragments;    -   wherein the expansion is configured to prevent clot fragment        migration;    -   wherein the distal end of the first monolithic structure        comprises an enclosed distal end said enclosed distal end        defining a surface the surface configured as a clot fragment        barrier surface;    -   wherein the clot fragment barrier surface comprises an        interconnected network of struts;    -   wherein the distal section of the clot engaging element is        configured to provide a three dimensional barrier to clot        migration;    -   wherein the device further comprises a elongate connector        element said elongate connector element comprising a proximal        end and a distal end, the proximal end connected to the second        monolithic structure and the distal end connected to the first        monolithic structure;    -   wherein the elongate connector element comprises a spring        element and said spring element is integral with the second        monolithic structure;    -   wherein the first monolithic structure and the second monolithic        structure are connected at their distal ends;    -   wherein the first monolithic structure and the second monolithic        structure are not connected at their distal ends; and/or    -   wherein the proximal sections of said first and second        monolithic structures are connected to a distal end of the        elongate member.

In another embodiment of the invention the treatment apparatus comprisesa clot retrieval device comprising:—an elongate member, and anexpandable clot engaging element configured to extend across the clot inits expanded state, the expandable clot engagement element comprising aproximal segment, a clot engaging segment and a distal segment, theproximal segment configured to extend proximal of the clot in use andthe distal end configured to extend distal of the clot in use, the clotengaging segment configured to engage with the clot in its expandedstate, the distal end comprising a fragment protection structure, thefragment protection structure comprising a plurality of strutsconfigured in a volumetric pattern.

Some optional features of this embodiment include:—

-   -   wherein the volumetric pattern comprises at least partially a        conically shaped volumetric pattern;    -   wherein the volumetric pattern comprises at least partially a        cylindrical volumetric pattern;    -   wherein the volumetric pattern comprises at least one plurality        of interconnected struts;    -   wherein the volumetric pattern comprises at least two        pluralities of interconnected struts;    -   wherein the volumetric pattern comprises a first plurality of        struts arranged about a first axis and a second plurality of        struts arranged about a second axis;    -   wherein the position of the first axis is moveable relative to        the position of the second axis;    -   wherein the first axis and the second axis comprise centre lines        and in use said centre lines may comprise straight and/or curved        centre lines;    -   wherein the centrelines are deflectable relative to one another;    -   wherein the volumetric pattern comprises a terminal end;    -   wherein the terminal end comprises a terminal junction for at        least some of said plurality of struts;    -   wherein the terminal end comprises a connection point at which        said plurality of struts are terminated and/or connected;    -   wherein the volumetric pattern comprises a first plurality of        struts, and a second plurality of struts;    -   wherein the second plurality of struts is at least partially        encompassed by the first plurality of struts;    -   wherein the second plurality of struts encircles the first        plurality of struts;    -   wherein the first plurality of struts is arranged about a first        axis and the second plurality of struts is arranged about a        second axis and said first and second axes are substantially        parallel;    -   wherein the first plurality of struts is arranged about a first        axis and the second plurality of struts is arranged about a        second axis and said first and second axes are substantially        parallel;    -   wherein the first plurality of struts comprises a conical shape;        and or    -   wherein the second plurality of struts comprises a spherical        shape, a flattened spherical shape, a cylindrical shape or a        spindle torus shape.

In another embodiment of the invention the treatment apparatus comprisesa clot retrieval device comprising:—an elongate member, and anexpandable clot engaging element comprising a first tubular structureand a second tubular structure, the first tubular structure at leastpartially encircling the second tubular structure, the first tubularstructure comprising a proximal end, a distal end, a proximaltermination and a distal termination, the second tubular structurecomprising a proximal end, a distal end, a proximal termination and adistal termination, the proximal termination of the first and secondtubular structures being connected to the elongate member and the distalterminations of the first and second tubular structures being connectedto each other.

Some optional features of this embodiment include:—

-   -   wherein the first tubular structure and the second tubular        structure comprise monolithic structures of interconnected        struts;    -   wherein the first tubular structure and the second tubular        structure comprise longitudinally extending structures;    -   wherein both the first tubular structure and the second tubular        structure comprise collapsed delivery configurations and        expanded deployed configurations and the first tubular structure        at least partially encircling the second tubular structure in        both the expanded configurations and the collapsed        configurations;    -   wherein one or both of the first tubular structure and the        second tubular structure comprise a proximal collar for        connecting one or both of the first tubular structure and the        second tubular structure to a distal end of the elongate member;    -   wherein the at least one proximal collar comprises a partial        collar; and/or    -   wherein the at least one proximal collar is cut from a hypotube        and encircles at least a portion of a distal end of the elongate        member.

In another embodiment of the invention the treatment apparatus comprisesa clot retrieval device comprising:—an elongate member, and anexpandable clot engaging element comprising a first tubular structureand a second tubular structure, the first tubular structure at leastpartially encircling the second tubular structure, the first tubularstructure and the second tubular structure connected to a distal end ofthe elongate member at a connection point, the first tubular structurecomprising a first proximal connecting strut and a first connectorelement, the second tubular structure comprising a second proximalconnecting strut and a second connector element, the first connectorelement encircling the second connector element at the connection point.

Some optional features of this embodiment include:—

-   -   wherein the first connector comprises a collar;    -   wherein the second connector comprises a collar or partial        collar; and/or    -   wherein the elongate member comprises a distal safety stop        configured to prevent distal movement of the first connector        and/or the second connector.

In another embodiment of the invention the treatment apparatus comprisesa clot retrieval device comprising:—an elongate member, and anexpandable clot engaging element configured to extend across the clot inits expanded state, the expandable clot engagement element comprising afirst luminal structure and a second luminal structure, the firstluminal structure being larger in diameter than said second luminalstructure, the distal end of said first luminal structure comprising aplurality of struts converging towards the axis of the first luminalstructure, the distal end of said second luminal structure comprising aplurality of struts diverging away from the axis of said second luminalstructure.

Some optional features of this embodiment include:—

-   -   wherein the distal end of said first and second luminal        structures are configured to form a three dimensional clot        fragment migration barrier;    -   wherein the distal end of said second luminal structure further        comprises an inflection region where a tangent to said plurality        of struts is substantially parallel to the axis of said second        luminal structure;    -   wherein the distal end of said second luminal structure further        comprises a converging region where said plurality of struts        converged on the axis of said second luminal structure;    -   wherein the distal end of said second luminal structure further        comprises a second distal junction where said plurality of        struts terminate;    -   wherein the distal end of said first luminal structure further        comprises a first distal junction where said plurality of struts        terminate;    -   wherein the first distal junction is distal of the second distal        junction; and/or    -   wherein the first distal junction is connected to the second        distal junction by a connector element.

In another embodiment of the invention the treatment apparatus comprisesa clot retrieval device comprising:—an elongate member, and a clotengaging element comprising a collapsed delivery state and an expandedclot engaging state, the clot engaging element configured to extendacross the clot in its expanded state, the clot engaging elementcomprising a proximal section, an intermediate section and a distalsection, the intermediate section comprising a luminal structure and thedistal section comprising an expansion region.

Some optional features of this embodiment include:—

-   -   wherein the diameter of the expansion region is larger than the        diameter of the intermediate section in the expanded state;    -   wherein the clot engagement element comprising plurality of        struts connected in a monolithic structure;    -   wherein the expansion region comprises a region of divergence        and a region of convergence;    -   wherein the expansion region comprises an inflection point        between the region of divergence and the region of convergence;    -   wherein the expansion region is integral with the intermediate        section;    -   wherein the expansion region comprises a transition section the        transition section comprising a plurality of struts connection        the expansion region to the intermediate section;    -   wherein the expansion region comprises a tapering distal end;    -   wherein the device comprises an elongate member connected to the        distal end of the expansion region; and/or    -   wherein in the expanded state the luminal structure is        configured to define a flow lumen through the clot.

In another embodiment of the invention the treatment apparatus comprisesa clot retrieval device comprising:—an elongate member, and a clotengaging element comprising a collapsed delivery state and an expandedclot engaging state, the clot engaging element configured to extendacross the clot in its expanded state, the clot engaging elementcomprising a proximal section, an intermediate section and a distalsection, the proximal section and the intermediate section comprising aluminal structure, the proximal section comprising a smaller diameterthan the intermediate section.

Some optional features of this embodiment include:—

-   -   wherein the diameter of the proximal section is less than 60% of        the diameter of the intermediate section;    -   wherein the diameter of the proximal section is less than 50% of        the diameter of the intermediate section;    -   wherein the diameter of the proximal section is less than 40% of        the diameter of the intermediate section;    -   wherein the diameter of the proximal section is less than 30% of        the diameter of the intermediate section;    -   wherein the diameter of the proximal section is less than 25% of        the diameter of the intermediate section;    -   wherein the diameter of the proximal section is less than 20% of        the diameter of the intermediate section;    -   wherein the proximal section comprises a proximal axis and the        distal section comprises a distal axis and the proximal axis is        offset relative to the distal axis in the expanded state.    -   wherein the proximal section comprises a first sub-structure and        the intermediate section comprises a second sub-structure;    -   wherein the luminal structure of proximal section extends        through the luminal structure of the intermediate section;    -   wherein the luminal structure of proximal section interconnects        with the luminal structure of the intermediate section;    -   wherein the clot engaging element comprises a transition section        interspersed between proximal section and the intermediate        section and configured to provide a smooth transition between        the proximal section and the intermediate section; and/or    -   wherein the distal section comprises a plurality of struts        configured in a closed distal end.

In another embodiment of the invention the treatment apparatus comprisesa clot retrieval device comprising:—an elongate member, and anexpandable clot engaging element configured to extend across the clot inits expanded state, the expandable clot engagement element comprising afirst luminal structure and a second luminal structure, the firstluminal structure being larger in diameter than said second luminalstructure and encircling at least a portion of the second luminalstructure, the second luminal structure extending substantially proximalof the first luminal structure.

Some optional features of this embodiment include:—

-   -   wherein the first luminal structure comprises a proximal        section, an intermediate section and a distal section and the        second luminal structure comprises a proximal section, an        intermediate section and a distal section;    -   wherein the intermediate section of the second luminal structure        extends substantially proximal of the intermediate section of        the first luminal structure;    -   wherein the proximal section of the second luminal structure        comprises a connection to a distal end of the elongate member;    -   wherein the proximal section of the first luminal structure        comprises a connection to a distal end of the elongate member;    -   wherein the proximal section of the first luminal structure        comprises a connection to the second luminal structure;    -   wherein the proximal section of the first luminal structure        comprises a connector extending from the intermediate section to        a connection point with the elongate member; and/or    -   wherein the connection point with the elongate member is        proximal of the second luminal structure.

In another embodiment of the invention the treatment apparatus comprisesa device for removing clot from a blood vessel comprising:—an elongatemember, and an expandable clot engaging element configured to extendacross the clot in its expanded state, the expandable clot engagementelement comprising a first luminal structure and a second luminalstructure, the first luminal structure being larger in diameter thansaid second luminal structure and encircling at least a portion of thesecond luminal structure, the second luminal structure comprising a clotcapture structure at its distal end, the clot capture structurecomprising a flared section.

Some optional features of this embodiment include:—

-   -   wherein the clot capture structure comprises a plurality of        struts and at least one fibre configured into a filter;    -   wherein in the expanded state the diameter of at least a portion        of the clot capture structure is similar to the diameter of the        blood vessel;    -   wherein in the expanded state the diameter of at least a portion        of the clot capture structure is larger than the diameter of the        second luminal structure; and/or    -   wherein in the expanded state the diameter of at least a portion        of the clot capture structure is similar to the diameter of the        first luminal structure.

In another embodiment of the invention the treatment apparatus comprisesa clot retrieval device comprising an elongate member, a firstexpandable member and a second expandable member; both expandablemembers having a proximal section, a body section, and a distal section,the body section of the first expandable member in the freely expandedstate being larger in diameter than that of the second expandable memberin the freely expanded state, and the proximal section of the firstexpandable member being distal of the proximal section of the secondexpandable member.

Some optional features of this embodiment include:—

-   -   wherein the distal section of the first expandable member        comprises a clot capture structure;    -   wherein the distal section of the second expandable member        comprises a clot capture structure;    -   wherein the clot capture structure comprises a plurality of        struts;    -   wherein the clot capture structure comprises a plurality of        struts and at least one fibre configured into a filter;    -   wherein the proximal end of the first expandable member is        connected to the distal section of the elongate shaft;    -   wherein the proximal end of the first expandable member is        connected to the second expandable member;    -   wherein the proximal end of the second expandable member is        connected to the distal section of the elongate shaft;    -   wherein the distal end of the first expandable member is not        connected to the distal end of the second expandable member;    -   wherein the distal end of the first expandable member is        connected to the distal end of the second expandable member;    -   wherein the body section of the second expandable member in the        freely expanded state is less than 50% of the diameter of the        body section of the first expandable member in the freely        expanded state;    -   wherein the body section of the second expandable member in the        freely expanded state is less than 40% of the diameter of the        body section of the first expandable member in the freely        expanded state;    -   wherein the body section of the second expandable member in the        freely expanded state is less than 30% of the diameter of the        body section of the first expandable member in the freely        expanded state; and/or    -   wherein the body section of the second expandable member in the        freely expanded state is less than 20% of the diameter of the        body section of the first expandable member in the freely        expanded state.

A method of using a clot retrieval device to retrieve a clot from avessel, said clot retrieval device comprising an expandable body and anelongate shaft, said method comprising: delivering the device through amicrocatheter to a target site, retracting the microcatheter to deploythe device at least partially within or beneath the clot, expanding aproximal section of the expandable member within a proximal section ofthe clot to a diameter smaller than that of the vessel, expanding adistal section of the expandable member distal of the clot to a diametersubstantially equal to that of the vessel, withdrawing the device andclot proximally and removing both from the patient.

Some optional features of this embodiment include:—

-   -   wherein the expandable body comprises an inner expandable member        and an outer expandable member;    -   wherein the expanded diameter of the inner expandable member is        smaller than that of the outer expandable member;    -   wherein at least a portion of the inner expandable member        extends within at least a portion of the outer expandable        member;    -   wherein at least a portion of the inner expandable member        extends proximal of the outer expandable member;    -   wherein the distal section of the expandable body comprises a        clot capture structure;    -   wherein the clot capture structure is connected to the inner        expandable member;    -   wherein the clot capture structure is connected to the outer        expandable member; and/or    -   wherein the elongate shaft extends outside of the patient in        use.

A clot retrieval device for removing occlusive clot from a blood vessel,the device comprising:—an elongate shaft; an inner elongate body havinga collapsed delivery configuration and an expanded deployedconfiguration; an outer elongate body at least partially overlying theinner elongate body; the outer elongate body being expandable relativeto the inner elongate body to a radial extent which is greater than theradial extent of the inner body in the deployed configuration; theproximal end of the outer elongate body being detachably fixed to thedistal end of the elongate shaft.

Some optional features of this embodiment include:—

-   -   wherein the proximal end of the outer elongate body comprises        two or more struts;    -   wherein detachment of the proximal end of the outer elongate        body from the distal end of the elongate shaft frees the        proximal struts to expand apart;    -   wherein the outer elongate body adopts a substantially        cylindrical or tubular shape upon detachment;    -   wherein the outer elongate body further comprises a closed        distal clot capture structure comprising a plurality of struts        converging at a terminal connection;    -   wherein the distal end of said plurality of struts are        detachable from the terminal connection;    -   wherein detachment of said plurality of struts from the terminal        connection frees the struts to expand apart;    -   wherein the device further comprises a detachment system; and/or    -   wherein the detachment system comprises a pull-wire, a        bio-absorbable collar or fibre, an electrolytic system or a        resistance heating system.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more clearly understood from the followingdescription of some embodiments thereof, given by way of example only,with reference to the accompanying drawings, in which:

FIG. 1a shows an isometric view of a clot retrieval device of thisinvention;

FIG. 1b shows a partially assembled isometric view of the proximal jointof the clot retrieval device of FIG. 1 a;

FIG. 1c is an isometric view of the proximal joint of the clot retrievaldevice of FIG. 1 a;

FIG. 1d is a section view through the device of FIG. 1 c;

FIG. 1e is an end view of the clot retrieval device of FIG. 1 a;

FIG. 1f is an isometric view of the distal end of the clot retrievaldevice of FIG. 1 a;

FIG. 1g is a plan view of the outer member of the clot retrieval deviceof FIG. 1 a;

FIG. 1h is a side view of the outer member of the clot retrieval deviceof FIG. 1 a;

FIG. 1i is a side view of the inner member of the clot retrieval deviceof FIG. 1 a;

FIG. 1j is an isometric view of the distal end of the inner member ofthe device of FIG. 1 a;

FIGS. 2a to 2f show a method of use of a device of this invention;

FIG. 3a shows the distal end of a clot retrieval device of thisinvention;

FIG. 3b shows the distal end of a clot retrieval device of thisinvention;

FIG. 4a is an isometric view of the distal end of a clot retrievaldevice of this invention;

FIG. 4b is a side view of the device of FIG. 4 a;

FIG. 5a is an isometric view of a clot retrieval device of thisinvention;

FIG. 5b is an isometric view of a clot retrieval device of thisinvention;

FIG. 6 is an isometric view of a clot retrieval device of thisinvention;

FIGS. 7a to 7e show a method of use of a device of this invention;

FIG. 8 shows a clot retrieval device deployed within a clot in a vessel.

FIG. 9 is a side view of a clot retrieval device of this invention;

FIG. 10a shows the distal end of a clot retrieval device of thisinvention;

FIG. 10b is an end view of the device of FIG. 10 a;

FIG. 10c is a detail view of an attachment feature;

FIG. 11a shows the distal end of a part of a clot retrieval device ofthis invention;

FIG. 11b is an end view of the device of FIG. 11 a;

FIG. 12 shows the distal end of a clot retrieval device of thisinvention;

FIG. 13a shows the distal end of a clot retrieval device of thisinvention;

FIG. 13b is an end view of the device of FIG. 13 a;

FIG. 14a is a side view of a clot retrieval device of this invention;

FIGS. 14b to 14d show side views of the clot retrieval device of FIG.14a in use;

FIGS. 15a to 15d show a method of use of a device of this invention;

FIG. 16 is an isometric view of the proximal joint of a clot retrievaldevice of this invention;

FIG. 17a is a side view of a clot retrieval device of this invention;

FIG. 17b is a detail view of a portion of the device of FIG. 17 a;

FIG. 18 shows the distal end of a part of a clot retrieval device ofthis invention;

FIG. 19 shows a clot retrieval device of the invention partiallyrestrained within a loading tool;

FIG. 20 shows a portion of a clot retrieval device of this invention;

FIG. 21a is a side view of a part of a clot retrieval device of thisinvention; and

FIG. 21b shows a developed view of the part of FIG. 20 a.

DETAILED DESCRIPTION

Specific embodiments of the present invention are now described indetail with reference to the figures, wherein identical referencenumbers indicate identical or functionality similar elements. The terms“distal” or “proximal” are used in the following description withrespect to a position or direction relative to the treating physician.“Distal” or “distally” are a position distant from or in a directionaway from the physician. “Proximal” or “proximally” or “proximate” are aposition near or in a direction toward the physician.

Accessing cerebral, coronary and pulmonary vessels involves the use of anumber of commercially available products and conventional proceduralsteps. Access products such as guidewires, guide catheters, angiographiccatheters and microcatheters are described elsewhere and are regularlyused in cath lab procedures. It is assumed in the descriptions belowthat these products and methods are employed in conjunction with thedevice and methods of this invention and do not need to be described indetail.

The following detailed description is merely exemplary in nature and isnot intended to limit the invention or the application and uses of theinvention. Although the description of the invention is in many cases inthe context of treatment of intracranial arteries, the invention mayalso be used in other body passageways as previously described.

A common theme across many of the disclosed designs is a dual layerconstruction in which the device comprises an outer expandable memberwithin which runs an inner expandable member, both members beingdirectly or indirectly connected to an elongate shaft, and a distal netor scaffold configured at the distal end of the device to prevent theescape of clot fragments. This distal net may be appended to either theshaft, the inner or the outer members or to several of these. A range ofdesigns are envisaged for each of these elements as described throughoutthis document, and it is intended that any of these elements could beused in conjunction with any other element, although to avoid repetitionthey are not shown in every possible combination. For example it isintended that the outer expandable member/outer cage of FIG. 1 could beused in conjunction with the inner expandable member of FIG. 4, or thedistal net of FIG. 13 could be connected to the distal end of the innerexpandable member of FIG. 5 in place of net 205 as shown.

Both the inner and outer expandable members are desirably made from amaterial capable of recovering its shape automatically once releasedfrom a highly strained delivery configuration. A superelastic materialsuch as Nitinol or an alloy of similar properties is particularlysuitable. The material could be in many forms such as wire or strip orsheet or tube. A particularly suitable manufacturing process is to lasercut a Nitinol tube and then heat set and electropolish the resultantstructure to create a framework of struts and connecting elements. Thisframework can be any of a huge range of shapes as disclosed herein andmay be rendered visible under fluoroscopy through the addition ofalloying elements (such as Platinum for example) or through a variety ofother coatings or marker bands.

The inner expandable member may in some cases form a generally tubularstructure and is ideally configured to expand to a lesser diameter thanthat of the smallest vessel in which it is intended to be used. Thisdiameter is typically less than 50% that of the outer expandable membermay be as low as 20% or less of the outer member diameter.

A range of different distal net or distal scaffolding zone designs aredisclosed, some of which incorporate strut elements from the frameworkof the outer and/or inner expandable members, and some of whichincorporate fine wires or fibres to provide added scaffolding withminimal impact of overall device profile or deliverability. Suitablematerials ideally have a high tensile strength so that a very fine wireor fibre with sufficient integrity for manufacturability and use can beproduced, such as for example polymers materials like UHMWPE, Aramid,LCP, PET or PEN, or metals such as Tungsten, MP35N, stainless steel orNitinol.

FIG. 1a shows one embodiment of a clot retrieval device of the presentinvention. The clot retrieval device 1 has an elongate shaft 6 having adistal end that extends interior of the artery and a proximal end thatextends exterior of the artery, a clot engaging portion configured atthe distal end of the elongate shaft 6 having an outer expandable member2 and an inner expandable member 3 to facilitate restoration of bloodflow through clot immediately after the clot retrieval device 1 isdeployed at an obstructive site. The outer member 2 and inner tubularmember 3 comprises a collapsed configuration for delivery and anexpanded configuration for clot retrieval, flow restoration andfragmentation protection. In one embodiment the inner expandable membercomprises a generally tubular body section.

The inner and outer members are preferably made of a super-elastic orpseudo-elastic material such as Nitinol or another such alloy with ahigh recoverable strain. Shaft 6 may be a tapered wire shaft, and may bemade of stainless steel, MP35N, Nitinol or other material of a suitablyhigh modulus and tensile strength. Shaft 6 may have indicator bands 7 onthe shaft to indicate to the user when the distal end of the device isapproaching the end of the microcatheter during insertion. These bandsare positioned so that as they approach the microcatheter hub orhaemostasis valve they indicate the distal tip of the device isapproaching the end of the microcatheter. These indicator bands can beformed by printing or removing or masking areas of shaft coating so thatthey are visually differentiated from the remainder of the shaft. Inanother embodiment the indicator bands 7 are recessed below the surfaceof the shaft to give tactile feedback to the user as they approach themicrocatheter.

Shaft 6 has a coil 4 adjacent its distal end and proximal of the outermember 2 and inner tubular member 3. This coil 4 may be metallic and maybe formed from stainless steel or from a more radiopaque material suchas platinum or gold for example or an alloy of such a material. Inanother embodiment the coil 4 may be coated with a low friction materialor have a polymeric jacket positioned on the outer surface of the coil.Adjacent to this coil 4 a sleeve 5 may be positioned on the shaft 6.This sleeve 5 may be polymeric and may be positioned over the taperedsection of the shaft. The sleeve 5 may be rendered radiopaque throughthe addition of a filler material such as tungsten or barium sulphate.The sleeve 5 and shaft 6 may be coated with a material to reducefriction and thrombogenicity. The coating may consist of a polymer, alow friction lubricant such as silicon, a hydrophilic or a hydrophobiccoating. This coating may also be applied to the outer member 2 andinner tubular member 3.

Referring especially to FIGS. 1b to 1d the shaft 6 may have integralcollars or a step feature 15 to assist the integrity of the jointsbetween the distal end of the shaft and the proximal ends of the innertubular member 3 and the outer member 2. The proximal end of the outermember 2 may comprise of a collar 12 and the proximal end of the innermember 3 may comprise of a partial collar 13. The inner member partialcollar 13 may be positioned on the shaft 6 proximal to the step feature15 and the collar 12 of the outer member may be assembled over thesefeatures to form a mechanical lock to prevent joint disassembly undertension. FIGS. 1b and 1c show the assembly of this joint while FIG. 1dis a section view of the joint showing the mechanical lock. This lock isformed as the collar of the outer member 12 is eccentric to the shaft 6and cannot slide over the step 15 of the shaft as long as the partialcollar of the inner tubular member 13 is in position. Adhesive may beadded to the assembled joint to further strengthen the joint and preventdisassembly under compression or other loading. In another embodiment asolder, weld or braze may be added to the assembled joint.

The collar of the outer member 12 is eccentric to the shaft 6 thereforein this embodiment a strut 14 is formed attached to the partial collarof the inner member 13. This strut 14 projects proximally and acts as alocating element for the proximal coil 4. When the proximal radiopaquecoil 4 is located on the proximal strut 14 and the shaft 6, the coil issubstantially concentric with the collar 12 of the outer member.Adhesive may be applied to the joint between the proximal coil and outermember collar to maintain the joint integrity. In another embodiment asolder, brazing or weld process may be used in this joint.

The outer member 2 is configured to self-expand upon release from arestraining sheath (such as a microcatheter) to a diameter larger thanthat of the inner tubular member 3. Expansion of the outer member 2causes compression and/or displacement of the clot during expansion.When an expandable body provides a high level of scaffolding the clot iscompressed. When an expandable body provides an escape path or openingthe expanding body will urge the clot towards the opening. However ifthe expandable body provides only modest scaffolding the clot will bedisplaced but since the clot has many degrees of freedom it may move ina variety of different directions and therefore cannot be controlled. Byproviding a tubular expandable body where the length of the tubularexpandable body is substantially as long as the length of the occlusiveclot or longer, many of the degrees of movement freedom available to theclot are removed. When, as with the current invention, inlet openings 22(as illustrated for example in FIG. 1g ) are provided in the outermember 2 these inlets 22 provide the primary movement freedom availableto the clot and so the expansion of the outer member 2 urges the clotinto the reception space 11. The outer member 2 has multiple inletmouths 22 to accept the clot. In this way inlet mouths 22 allow portionsof the clot to enter reception space 11 of the outer member 2, and thusallow the clot to be retrieved without being excessively compressed.This is advantageous because we have discovered that compression of clotcauses it to dehydrate, which in turn increases the frictionalproperties of the clot, and increases its stiffness, all of which makesthe clot more difficult to disengage and remove from the vessel. Thiscompression can be avoided if the clot migrates inward through the wallof the outer member 2 as the porous structure migrates outward towardsthe vessel wall.

FIG. 1g shows a plan view and FIG. 1h shows an elevation of the outermember 2. The inlet mouths 22 provide the added benefit of allowing theouter member 2 when retracted to apply a force to the clot in adirection substantially parallel to the direction in which the clot isto be pulled from the vessel (i.e. substantially parallel to the centralaxis of the vessel). This means that the outward radial force applied tothe vasculature may be kept to a minimum, which in turn means that theaction of the clot retrieval device 1 on the clot does not serve toincrease the force required to dislodge the clot from the vessel, thusprotecting delicate cerebral vessels from harmful radial and tensileforces.

Outer member 2 comprises proximal struts 20 connected at their proximalends to a collar 12 and at their distal ends to a first expandablemember 26. The proximal struts 20 may have a tapered profile to ensure agradual stiffness transition from the shaft 6 to the clot engagementsection of the device. The first expandable member 26 is connected to asecond expandable member 27 by two connecting arms 29, which run from aproximal junction 39 to a distal junction 40. In one embodiment theseconnecting arms comprise generally straight struts running parallel tothe central axis of the device. In other embodiments these connectingarms may comprise a plurality of struts configured in one or more cells,or may comprise curved or spiral arms. The region between the first andsecond expandable member comprises two inlet mouths 22 through whichclot may pass and enter the reception space 11 defined by the regionbetween the inner and outer members.

The second expandable member 27 is in turn connected to a thirdexpandable member 28 by two connecting arms 30, which run from aproximal junction 41 to a distal junction 42. In one embodiment theseconnecting arms comprise generally straight struts running parallel tothe central axis of the device. In other embodiments these connectingarms may comprise a plurality of struts configured in one or more cells,or may comprise curved or spiral arms. The region between the second andthird expandable member comprises two inlet mouths 22 through which clotmay pass and enter the reception space 11 defined by the region betweenthe inner and outer members. The connecting arms between the firstexpandable member 26 and the second expandable member 27 may besubstantially aligned with the connecting arms between the second andthird expandable members 27,28 to align the neutral axis of theexpandable members 26,27,28 during bending. In another embodiment theconnecting arms between the first expandable member 26 and the secondexpandable member 27 may be aligned at an angle, such as 90° to theconnecting arms between the second and third expandable members 27,28.

The first expandable member 26 comprises a series of interconnectedstruts, with certain struts such as strut 43 terminating in crowns withno distal connecting elements, and other struts such as 44 terminatingin junction points such as 45 and 46. The second expandable member 27comprises a series of interconnected struts, with certain struts such asstrut 47 terminating in crowns with no distal connecting elements, andother struts such as 48 terminating in junction points. One or moreexpandable members may comprise marker bands or radiopaque features suchas gold or platinum marker or coils. In this embodiment a gold ovalmarker 25 is shown fixed in an eyelet on a strut in the third expandablemember 28. The gold marker is positioned to indicate to the user thedistal end of the barrel section of the outer member to aid in accuracyof deployment. The struts in the expandable members may be configured sothat during loading, multiple crowns do not align at the same distancefrom the proximal collar, for example 45 and 50. During loading orresheathing, a higher force is generally required to load a crown than astrut into the sheath, therefore if multiple crowns are loaded at thesame time the user may notice an increase in loading force. Byoffsetting the crowns by making alternative struts 44 and 51 differentlengths the loading force may be reduced and the perception to the useris improved.

The distal end of the third expandable member 24 comprises acircumferential ring of struts 23 connected to a series of struts 24that ultimately terminate at a distal junction point 9, thus defining aclosed end to the outer member. This series of struts may comprise agenerally conical shape as shown in FIGS. 1a, 1f, 1g and 1h , or inother embodiments may comprise a generally flat plane which may beinclined or may be normal to the longitudinal axis of the device. In oneembodiment (as shown) the distal junction point 9 comprises a collar.Struts 24 and 49 may be tapered to a narrower width than those of themore proximal struts comprising the body of the first and secondexpandable members, thus creating a gradual transition in the stiffnessof the device both in the expanded and collapsed states.

FIG. 1e shows the closed end of the outer expandable member 2 whichprevents the egress of clot or clot fragments that have entered thereception space 11 between the inner and outer members. The expandeddistal struts 10 of the inner member act as an additional threedimensional filter in combination with the closed distal end of theouter member 2 to further prevent the egress of clot or clot fragments.In certain embodiments this distal section may comprise fibre attachmentpoints such as eyelets 17 or other fibre attachment features and fibresmay be connected to the distal section at these attachment points tocreate a distal net.

FIGS. 1i and 1j show views of the inner tubular member 3. The innertubular member 3 comprises a collapsed configuration for delivery and anexpanded configuration for flow restoration and fragmentationprotection. The inner tubular member 3 may comprise an elastic orsuper-elastic or shape-memory metallic structure and may furthercomprise a polished surface such as an electro-polished surface. Theinner tubular member 3 is configured so as to provide a flow lumenthrough the device 1 to facilitate the immediate restoration of bloodflow past the clot upon deployment. In one embodiment the inner tubularmember 3 is configured to scaffold said flow lumen through the clot toprevent the liberation of fragments which might otherwise lodge in thedistal vasculature. The inner tubular member 3 consists of a series ofconnected struts 31 that may contact a clot when initially deployed in atarget vessel within the clot. The contact of the struts 31 of the innertubular member 3 with the clot provides additional grip and assists inthe initial dislodgement of the clot from the vessel when the device isretracted.

Inner tubular member 3 comprises a generally cylindrical section ofinterconnected struts 31, which is connected at its proximal end bystrut 34 to partial collar 13. The distal end of the inner tubularmember 3 consists of an expansile section formed from expanded struts 10which have a diameter greater than that of the body section of the innertubular member 3. These expanded struts are connected to a coil section18 which in this embodiment is laser cut from the tubing that the innertubular member 3 is also cut from during processing. The distal end ofthe coil 18 has a castellated profile 35 which is joined to the distalcollar 9 of the outer member 2 during assembly. The distal end of thecoil 18 on the inner tubular member 3 is bonded to the distal collar ofthe outer member 2 by adhesive. The castellated feature 35 on the innertubular member 3 facilitates this adhesive bond and improves thestrength of the bond by providing a reception space 38 for the adhesivewithin the collar and preventing it from wicking into the coil area. Inanother embodiment this joint may be assembled using a solder, weld orbraze process.

The outer member 2 and the inner tubular member 3 are joined at theproximal and distal ends during assembly thereof to minimise tensionwithin the members during use, the length of the outer member 2 shouldbe substantially the same as the length of the inner tubular member 3 inthe freely expanded configuration and the loaded configuration. Theexpanded struts 10 of the inner tubular member 3 elongate during loadingso that the lengths of the inner and outer members are equal when fullyloaded in a microcatheter. Length differentials between the innertubular member 3 and the outer member 2 can still occur when the deviceis deployed in a small vessel or during the loading or deploymentprocess. The coil 18 at the distal end of the inner tubular member 3 canaccommodate minor length differentials by stretching without applyingsignificant tensile or compressive forces to the device. In anotherembodiment this coil could be formed separately to the inner tubularmember 3 and then be assembled to it. The coil could be formed from astainless steel material, a polymer or from a more radiopaque metal suchas gold or platinum or an alloy of such a material. The coil could alsobe replaced with a longitudinal length of an elastic material such as alow modulus polymer or elastomer.

FIG. 1f shows the distal end of the assembled device 1 and FIG. 1j showsthe distal end of the inner tubular member 3. The distal end of theinner tubular member 3 also comprises a distal arm 32. The arm may belaser machined from the same tube as the rest of the inner tubularmember. A radiopaque coil 8 (which may be platinum or gold or an alloyof same) is positioned over the distal arm 32 and butts against thedistal collar 9 of the outer member 2, where it is connected by anadhesive joint to the collar 9 and arm 32. The distal tip of the arm 32and the distal end of the radiopaque coil 8 are also connected by anadhesive joint. The distal arm 32 has a profile 37 at the distal tipwhich facilitates the adhesive joint by providing a reception space 36for the adhesive within the radiopaque coil 8 and preventing theadhesive wicking up the coil. This adhesive joint forms a substrate forthe application of additional adhesive to form a semi-sphericalatraumatic tip 19 on the distal end of the device.

In other embodiments the inner tubular member may not be connected tothe distal end of the outer member at all, or may be constrained withinthe outer member without being fixedly attached. In other embodimentsthe inner tubular member may have a non-cylindrical cross-section, maybe non-uniform in diameter, and may have tailored strut patterns toprovide regions of differing radial force or flexibility.

FIGS. 2a-2f shows a method of use of a device of this invention. Aguidewire 63 and microcatheter 62 are inserted in the artery 60 and areadvanced across the obstructive clot 61 using conventionally knowntechniques. When the microcatheter 62 is positioned distal to theocclusive clot 61, the guidewire 63 is removed from the artery 60 toallow the clot retrieval device 1 be advanced through the microcatheter62. The device 1 is advanced in a collapsed configuration until thedistal tip of the device 1 reaches the distal end of the microcatheter62. The microcatheter 62 is retracted while the position of device 1 ismaintained to deploy the clot retrieval device 1 across the clot 61 in amanner that the distal end of the device 1 is preferably positioneddistal of the clot 61. The device 1 expands so that the outer member 2engages with the occlusive clot and the inner tubular member 3 expandsto engage the clot and provide a flow channel to restore blood flow in acontrolled manner through the occlusive clot 61. The device 1 may beallowed to incubate for a period of time within the clot 61 if desired,as controlled flow has been restored through the inner tubular member 3.Retracting the device 1 dislodges the clot from its position in theartery 60 and further withdrawal of the device retrieves the clot 61until it can be retrieved into the guide catheter 64 or introducersheath. FIG. 2f illustrates the clot engaged with the device duringretrieval into the guide catheter 64. The clot is partially located inthe inlet openings 22 of the device 1 and also partially located in thereception space 11 defined by the region between the inner and outermembers. Clot fragments 65 are shown trapped in the distal end of thedevice 1 where the closed end of the outer member and the expandedstruts of the inner member have prevented the fragments from beingreleased in the blood flow. Flow occlusion, aspiration and otherstandard techniques may be used during the clot retrieval process. Thedevice 1 may be rinsed in saline and gently cleaned before reloading inthe insertion tool. The device 1 may be reintroduced into themicrocatheter to be redeployed in additional segments of occlusive clot,if required.

An isometric view of the distal end of another embodiment of a clotretrieval device similar to device 1 is shown in FIG. 3a . In thisembodiment there is no fixed distal connection between the outer member82 and the inner tubular member 83. The expanded struts 80 or the distalend of the body section of the inner tubular member 83 terminate at acollar 87 which can slide on a wire 86 to accommodate lengthdifferentials between the inner and outer members that occur during usewhen the device is expanded, collapsed or deployed in a small vessel.The wire 86 may be joined to the outer member 82 at the collar 89 by anadhesive, solder, weld or braze joint. The wire 86 comprises a step,collar or flare feature 88 which prevents the collar 87 of the innertubular member 83 disengaging from the wire 86. The wire 86 may bemetallic and be formed from stainless steel or Nitinol, alternatively itmay be formed from a high durometer polymer such as PEEK or Polyimide oras a polymer jacketed metallic wire. The wire 86 may also be formed bylaser cutting and be cut from the same tubing that the outer member 82is processed from. In this case the wire 86 would be an integral part ofthe outer member 82 and be connected at the distal collar 89. Toassemble the inner tubular member 83 and the wire 86, a slot may be cutin the collar 87 of the inner tubular member 83. The step 88 on theproximal end of the wire 86 may have a radiused atraumatic proximal endand may be connected by a fibre to another part of the device tominimise the degrees of freedom of the wire to prevent the proximal endof the wire protruding through the outer member 82 when the device is ina curved configuration. This fibre may be connected to a proximal collarof the inner or outer members and may be formed from an elasticmaterial.

An isometric view of the distal end of another embodiment of a clotretrieval device similar to device 1 is shown in FIG. 3b . In thisembodiment there is no distal connection between the distal ends of theinner 83 and outer expandable 82 members. In this embodiment the bulgedor flared end 80 of the inner expandable member 83 acts as a guide tokeep the inner member within the outer member. This embodiment differsfrom that of device 1 in that it has no distal tip—rather a rounded end89 is positioned at the distal most point of the outer member to renderit atraumatic to the vessels in which it is used. In other similarembodiments the inner member bulge or flared section 80 comprises strutsconfigured in a spiral shape, or configured in cellular patterns so thatthe struts of the bulge or flare are not parallel to those of theadjacent portion of the outer member. Ideally the struts of the bulge orflare are perpendicular, or closer to perpendicular than parallel tothose of the adjacent portion of the outer member. In this way the bulgeor flare will be prevented from moving outside the outer member when thedevice is positioned in bends.

Another embodiment of the device is shown in FIGS. 4a and 4b , whereFIG. 4b is a side view of the device and FIG. 4a is an isometric view ofthe distal end of the same embodiment. In this embodiment an elasticfibre 89 may be connected to the proximal collar 12 of the outer member2 or the proximal end of the inner tubular member, and to the distalcollar 9 of the outer member 2. This fibre 89 is positioned inside theinner diameter of distal collar 90 of the inner member 3 and facilitatesthe collar 90 sliding proximally or distally on the elastic fibre 89.Therefore as the length differential between outer member 2 and innermember 3 changes during use when the device is expanded, collapsed ordeployed in a small vessel, the fibre 89 can elongate or contract asnecessary to maintain the collar 90 of the inner member 3 in a generallycentral location in the outer member 2. The fibre may be formed from alow durometer polymer material, a rubber or elastomer or be acombination of a high durometer fibre and a small diameter coil spring.The coil spring could be formed from a metallic material or a polymer ora combination of both such as a polymer jacketed wire.

Referring now to FIG. 5a , there is shown a clot retrieval device 150comprising an elongate shaft 151, an inner expandable member 153, and anouter expandable member 154. The outer expandable member comprises aplurality of struts 158 and connecting elements 157, and furthercomprises a distal scaffolding zone 155 and a distal tip 156. In theembodiment shown the outer expandable member is connected to the innerexpandable member by connecting arms 159 at connecting junctions 160. Inanother embodiment the shaft 151 may extend through the inner expandablemember and the outer expandable member may be connected to a distalregion of said shaft. In yet another embodiment the portion of the innerexpandable member proximal to the outer expandable member may be formedfrom the same piece of material (for example a single piece of nitinoltubing) as the outer expandable member, and the portion of the innerexpandable member distal to the proximal end of the outer expandablemember may be formed from a separate piece of material. The innerexpandable member is connected to shaft 151 at connection point 152. Theproximal end of the elongate shaft is configured to extend outside ofthe patient so that the user can use it to control the clot retrievaldevice position within the patient.

Each of the shaft and inner and outer expandable members may beconstructed in a variety of manners as disclosed herein. This dual layerconstruction is intended to allow clot to enter through the largeopenings 161 of the outer expandable member and sit in the receptionspace 162 provided between the two expandable members. The inner memberhas a denser scaffold than that of the outer such that the clot isprevented from entering its lumen, thus creating a flow channel acrossthe clot once the device is deployed across it. The long proximalportion of the inner member can be constructed with a very small volumeof material, as it only expands to a fraction of the diameter of theouter member, and can thus be highly flexible in both the collapsed andexpanded states. A significant benefit of this proximally extendingmember is that it allows a flow channel to be created across very longclots without overly compressing the clot or engaging with the vesselwall.

The distal scaffolding zone may comprise a generally conical tapering ofthe distal end of the outer member defined by a plurality of strutelements. In one embodiment one or more fibres are attached to thedistal region of the outer member to increase the scaffolding byreducing the pore size of the openings in a manner similar to that shownin FIG. 12. In another embodiment the outer member may terminate moreabruptly in a manner similar to that shown in FIG. 10a , in which designfibres or wires may be connected to the outer member to span its distalend and create a fragment capture zone. These fibres or wires may alsobe connected to the inner member, or indeed in yet another embodimentsimilar to that shown in FIG. 5b the distal scaffolding zone or distalnet may be connected only to the inner member.

FIG. 5b shows another clot retrieval device 200 of this inventionsimilar to device 150 of FIG. 5a but in which the distal net orscaffolding zone is attached to the inner expandable member rather thanthe outer, and in which the outer expandable member is attached to theshaft 201 rather than to the inner member. The inner expandable member203 is attached to elongate shaft 201 at connection 202. This connectionmay comprise a collar. The outer expandable member 204 is connected byconnecting arms 206 to the distal segment 207 of shaft 201 at point 209.Radiopaque markers 208 are attached to the distal end of outer member204. A distal net 205 is attached to the distal end of the inner member203.

The outer expandable member 204 comprises clot scaffolding regions 210and inlet openings 211 such that clot is urged by the scaffoldingregions to flow through the openings into the reception space 212between inner and outer members as described in more detail elsewhere.

In other embodiments the inner and outer members and distal net maycomprise any of the designs disclosed elsewhere herein for theseelements. In this embodiment connecting arms 206 of the outer memberpass through openings in the framework of inner member 203 and join tothe shaft, while in other embodiments the outer member may be attacheddirectly to the inner member. In yet another embodiment the portion ofthe inner expandable member proximal to the outer expandable member maybe formed from the same piece of material (for example a single piece ofnitinol tubing) as the outer expandable member, and the portion of theinner expandable member distal to the proximal end of the outerexpandable member may be formed from a separate piece of material.

FIG. 6 shows another clot retrieval device 250 of this invention inwhich the inner expandable member and the outer expandable member do notoverlap and are formed into a continuous framework which could be madefrom a single piece of material in a monolithic structure. Theexpandable body 257 comprises a proximal portion 252 which is smaller inexpanded diameter than distal section 253, such that distal section 253may be configured to engage with the wall of the vessel in which thedevice is intended to be used, while proximal section 253 may beconfigured to expand to a diameter smaller than said vessel, such thatproximal and distal portions perform somewhat in the manner of thepreviously described inner and outer members. Proximal portion 252 ofexpandable body 257 is attached to the distal portion of elongate shaft251. The distal struts 255 of the expandable body may in otherembodiments be terminated in a conical scaffolding region similar tothat shown in FIG. 1a , or may be attached to a distal net such as forexample that shown in FIG. 4.

FIGS. 7a-7e show a method of use of a device of this invention. Forillustration, the device 200 of FIG. 5 is shown being used to retrieve along occlusive clot 301 from vessel 300. In the case of an intracranialocclusion a variety of access routes are possible, including a directstick into the carotid artery, a brachial approach, or a femoral access.Once access has been gained to the arterial system using conventionaland well understood techniques, a guide catheter or long sheath 307 (notshown in FIGS. 7 a-d) is typically placed as close to the occlusive clotas practical. In the case of a middle cerebral artery occlusion theguide catheter might be placed in the internal carotid artery proximalof the carotid siphon. A microcatheter 302 is then advanced across clot301 with the aid of a guidewire 303. In some cases an additionalcatheter (which may be known as a Distal Access Catheter or DAC) may beused in a triaxial system such that the microcatheter is advancedthrough the DAC, which is in turn advanced through the guide catheter orlong sheath. Once the microcatheter tip has been advanced across anddistal of the clot the guidewire is removed and the clot retrievaldevice 200 is advanced through the microcatheter until it reaches itsdistal end as shown in FIG. 7c . The microcatheter is then retracted,allowing the clot retrieval device 200 to expand within and either sideof the clot as shown in FIG. 7d . Because the device is configured witha long inner expandable member 203, this member can extend proximal ofeven a very long clot and upon device deployment the expansion of thismember creates a flow channel through the clot, restoring flow to thevascular bed distal of the clot and reducing the pressure gradientacross the clot. This reduction in pressure gradient reduces the forcerequired to disengage the clot from the vessel wall and retract itproximally. The scaffolding regions 210 of the outer expandable member204 expand within the distal portion of the clot applying a compressiveforce to discrete regions of the clot, thus urging the clot to flow awayfrom these regions, through the inlet openings 211 and into thereception space 212 between the inner and outer members. This causescompression in discrete regions 304 of the clot, but causes minimalcompression in regions 305 of the clot, or in the region proximal of theouter member. Minimizing compression on the clot in this way minimizesthe forces applied radially outward to the vessel wall, which in turnreduces the frictional force to be overcome when retracting the clot.Because the inner member has created a channel through which blood canpass to the distal vascular bed, the device can be safely left in placefor a dwell period prior to withdrawal. This dwell period is desirablygreater than one minute and may be as long as 30 minutes or more.Allowing the device to sit in this way allows the clot to flow into thedevice which facilitates gripping it securely for retrieval. It alsoallows the distal vascular bed to be gently perfused with freshoxygenated blood rather than be exposed to a sudden jump in pressure andflow as would be the case if the clot were immediately removed or if thedevice were to compress the clot so much that a very large flow channelwas created upon deployment. Once the dwell period has elapsed thedevice and microcatheter (not shown) can be retracted back into eitherthe DAC or guide/sheath as shown in FIG. 7e . This may be done with theaid of aspiration through the guide/sheath or DAC to assist in retaininga firm grip on the clot and avoiding fragment loss, however thedisclosed designs which grip the clot securely and house the clot safelywithin a reception space and further comprise a distal net orscaffolding region have the advantage that they can be safely usedwithout aspiration. The distal net 211 may be spaced apart from thedistal end of the outer member as shown such that it is optimallypositioned to trap any fragments released from the clot duringretraction even if these fragments originate from that portion of theclot not fully housed with reception space 212. Such a fragment 308 isshown in FIG. 7 e.

FIG. 8 shows another clot retrieval device 350 of this invention inwhich the inner expandable member 352 is designed to be particularlyflexible. The device comprises an inner expandable member 352, an outerexpandable member 353, a distal protection net 356 and an elongate shaft357. The inner and outer expandable members are attached to a distalsection of the shaft, and the distal protection net is attached to theend of the inner expandable member. The device is shown deployed in avessel 351 within a clot 354 and 355. The compliant inner member isdisplaced in one direction by one portion 354 of the clot, and in adifferent direction by a second portion 355 of the clot.

In the embodiment shown the compliance of the inner member is madepossible by the design of the framework of struts and connectors fromwhich this member is formed. The inner member illustrated in FIG. 8comprises a series of generally cylindrical rings 358 formed by struts359 and connected to an adjacent ring by connectors 360. In order tooptimize the clot scaffolding properties of the member all of the crownsof each ring 359 are connected to another crown by a connector 360, thuscreating a dense, closed cell structure. However such a structure isgenerally less flexible than an open cell structure in which not allcrowns are connected. This problem is overcome by inclining theconnectors at an angle to the axis of the inner member so that when themember is placed in a bend the resultant load on the connectors is aflexural load rather an axial compressive or tensile load. For a givenbend angle this flexural load can be accommodated at a much lower strainlevel than would be possible were the connector aligned with the axis ofthe member, therefore the resultant inner member can be flexed and bentmuch more easily than would be the case with conventional axiallyaligned connectors.

In yet another embodiment the inner member is constructed in a similarfashion to that described above except that the connectors alternate indirection between each adjacent ring—for example all of the connectorsbetween the first and second rings may be oriented clockwise, while allof the connectors between the second and third rings may be orientedanticlockwise. Thus when the device expands or contracts each ringtwists relative to its adjacent ring, but each twist counterbalance thenext so that minimal twisting occurs to the distal end of the innermember relative to the proximal end.

In yet another embodiment the inner member comprises a closed cellpattern of cells, each cell bounded by struts, and the cells configuredin a generally spiral pattern around the circumference of the member.

In another embodiment the inner member comprises a braided structure,formed from one or more wires. The braided structure comprises a seriesof opposing spirals, with multiple overlap points where one wire crossesover another. At least some of these crossover points are not fixedattachment points, so that the member can easily accommodate a bend by asliding action of one wire over another at these crossovers.

In yet another embodiment the inner member comprises an open cellframework of struts and connectors.

FIG. 9 shows another clot retrieval device 400 of this invention inwhich the inner expandable member 406 is offset relative to the outerexpandable member 403. Such a construction may be desirable for severalreasons. One such reason is to aid manufacturability in the event thatthe outer member is formed from a large diameter tube or from a flatsheet and thus has a proximal end or apex 407 that is offset from thecentreline of the outer member and is in or close to the cylindricalplane defined by the outer surface of the member. In the embodimentshown the inner member 406 and outer member 403 are connected at theirproximal ends to the distal end of shaft 401 at connection point 407,which is offset from the central axis of the expanded outer member, andhence of the vessel in which the device is intended to be deployed. Adistal net 405 is appended to the distal end of the outer member 403.

FIGS. 10a (side view) and 10 b (end view) show the distal region ofanother clot retrieval device 450 of this invention in which a distalfragment protection feature is created by the attachment of shaped wiresor fibres 455 between eyelets 453 on crowns 456 of outer member 452 andeyelets 454 on crowns 457 of inner member 451. The shaped wires orfibres may be formed in a variety of shapes to optimize the coverage ofthe aperture at the end of the device. In the embodiment shown the shapeis generally two dimensional sinusoidal pattern. In another embodimentthe shape may three dimensional and more similar to that shown in FIG.12. The wires or fibres may be made from polymer materials like UHMWPE,Aramid, LCP, PET or PEN, or metals such as Tungsten, MP35N, stainlesssteel or Nitinol. An advantage of using Nitinol or a similar shapememory material is that the wire can recover to its formed “memorized”shape upon deployment. The wires or fibres may in other embodiments beattached to features on the framework of the inner or outer membersother than eyelets in the crowns, or may be simply passed through cellsof either member to create an attachment location.

FIG. 10c depicts an alternative connection hook 477 design that could beincorporated in a strut 475 of an inner or outer expandable member topermit the attachment of a wire or fibre without needing to thread anend of the wire or fibre through an eyelet. Instead the wire or fibremay be slotted into place. The recesses created by lips 476 and 478 aidin retaining the wires or fibres in position.

FIGS. 11a (side view) and 11 b (end view) show the distal region ofanother clot retrieval device 500 of this invention in which a threedimensional distal fragment protection feature is created by a bulgedframework of struts. Expandable member 501 comprises multiple crowns504, to which are connected a plurality of filter arms 502, whichterminate at connection point 503. The filter arms are flared radiallyoutward to form a bulged shape of a larger diameter than the body of theexpandable member 501, which might in some embodiments be the innerexpandable member of a clot retrieval device. The flared filter arms 502are also spiralled so that in end view they cross over one another atleast at points 505 as shown in FIG. 11b . This spiralling serves toreduce the area of the openings 506 through which fragments of clotmight otherwise escape. In another embodiment the filter arms are notspiralled. In yet another embodiment the filter arms originate fromcrowns which are themselves expanded to the diameter of the bulge. Inyet another embodiment the enclosed space 507 formed beneath the bulgeof the filter arms is filled with a second material. In one embodimentthis second material comprises a filter mesh, which may be formed of oneor more lengths of wire of a material such as Nitinol, similar to thedesign shown in FIGS. 13a and 13 b.

FIG. 12 shows the distal region of another clot retrieval device 550 ofthis invention in which an inner expandable member incorporating a threedimensional distal fragment protection feature 500 (previously shown anddescribed) is contained within an outer expandable member 551 comprisinga conical tapering distal end 552. The resultant structure providesmultiple layers of fragmentation protection and is particularlyaffective at dealing with large fragments and large volumes of fragmentswithout the fragments gathering together in one point and causing anobstruction to flow through the device. The distal conical section ofthe outer expandable member 551 comprises a plurality of struts 552,which in turn comprise a plurality of eyelets 554, through which arethreaded one or more fibres 555 to create a scaffolding net across thelumen of the vessel in which the device is deployed.

FIGS. 13a (side view) and 13 b (end view) show the distal region ofanother clot retrieval device 600 of this invention. The devicecomprises an outer expandable member 601 and an inner expandable member606. The inner expandable member 606 incorporates a bulged or flareddistal section 602, similar to that of part 500, within which isretained a mesh-like structure 603 formed from wire or fibre. In oneembodiment the opening angles of the cells of the inner and outerexpandable members are configured such that the outer memberforeshortens to a greater degree than the inner member upon expansion,with the result that the bulged filter section 602 is situated beneathor proximal to distal crown 604 of the outer member when in thecollapsed/wrapped down configuration for delivery, but is situateddistal to crown 604 when in the expanded configuration. This change inrelative positions is advantageous to minimize device length and parkingspace during delivery and deployment, and to maximise the effectivenessof the fragment protecting filter during retrieval. In one embodimentthe mesh-like structure 603 is formed from randomly curled fine wire,where this wire is preferably Nitinol wire, and is preferably of lessthan 50 microns in diameter, and most preferably less than 25 microns indiameter. In another embodiment the mesh-like structure 603 is formedfrom a polymer fibre, where this fibre is preferably an Aramid, LCP,UHMWPE, PET or PEN and is preferably of less than 50 microns indiameter, and most preferably less than 25 microns in diameter. Thefibres or wire may be randomly curled and/or twisted to occupy the spacewithin the bulge, or they may be shaped into a specific pattern. Thefibre or wire may be attached to the inner member or may simply beretained by the struts forming the outer periphery of the bulge 602.Bulge 602 may be formed from three or more struts, and these struts maybe generally aligned with the central axis of the device or may becurved or spiralled around this axis as previously shown.

FIG. 14a shows another clot retrieval device 650 of this invention inwhich the outer expandable member 653 is detachable from the rest of thedevice. FIG. 14b shows the same device following detachment of the outermember. FIGS. 14c and 14d together show the inner expandable memberbeing retracted from the patient leaving the outer expandable memberbehind. This detachment feature enables a user to elect to leave theouter member deployed within a vessel as an implant, which might bedesirable in the case of an atherosclerotic or thrombotic occlusion, orin the event that the device become so firmly lodge in the clot that theuser felt it would be unsafe to pull the entire device any harder. Theprinciples illustrated could be applied to any of the inner and/or outerexpandable members shown elsewhere herein. Device 650 comprises an outerexpandable member 653 and an inner expandable member 656, both connectedto the distal end of an elongate shaft 651 at proximal joint 657. Theouter expandable member comprises a plurality of struts 658 andconnectors 659, with a series of proximal terminations 652 and distalterminations 655. In the configuration prior to detachment the proximalterminations 652 are attached together and to shaft 651 at proximaljoint 657, and the distal terminations 655 are attached together atdistal joint 660.

In the embodiment shown the proximal joint 657 is generally concentricwith the device and is radially displaced from the side wall of thevessel. Therefore the proximal struts 662 would obstruct the vessellumen if left unaltered, causing potential recrossing difficulties andacting as a potential nidus for future clot formation. To address thisissue the proximal terminations 652 separate upon detachment from theproximal joint 657, freeing the proximal struts (which are heat set toremember a preferred radially outwardly projecting configuration) toexpand and appose the vessel wall or clot. A variety of means can beemployed to detach the proximal joint and terminations, including:electrolytically, resistance heating of a low melt joining material, orother mechanical pull-wire or twisting mechanism. An example of a pullwire joint is shown in FIG. 16. In another embodiment the proximal joint657 is offset from the centreline of the device and vessel and isgenerally in line with the plane of the outer circumference of the outermember, in which case it is not necessary to separate the proximalstruts 662 as they will self align with clot and/or vessel wallautomatically upon detachment of the proximal joint.

In one embodiment the distal terminations 655 are held together by abioabsorbable fibre or collar, which is configured to dissolve after aperiod of time in contact with blood and thus allow the terminations toseparate and the distal cone to expand towards a cylindrical shape andappose the vessel wall. This time period is ideally greater than 30minutes and less than 7 days, and is most preferably between 1 and 3hours. In other embodiments the distal joint is connected to the distalend 661 of the inner expandable member in such a way that retraction ofthe inner expandable member relative to the outer expandable memberdisconnects the distal joint and allows the distal cone of the outermember to expand. In yet other embodiments the distal terminations arereleased by means similar to that described above for the release of theproximal terminations.

FIGS. 15a-15d show a method of use of a detachable device 700, similarto previously described device 650. Device 700 comprises an outerexpandable member 704, an inner expandable member 705, a shaft 709 and adistal net 706. Distal net 706 is attached to the distal end of theinner expandable member 705, and the proximal end of the inner member isattached to the distal region of shaft 709. The proximal end of theouter expandable member is attached to the distal end of the shaft 709at proximal joint 708, and is detachable in the same manner as thatpreviously described for device 650. The distal end of the outerexpandable member differs from that of device 650 in that it terminatesin crowns 710 and not in a conical section, and therefore does notrequire detachment and further expansion if the device is to be left inplace as an implant.

The method of use is similar to that described in relation to FIG. 2 andFIG. 7 in that access is gained and a microcatheter 703 is advancedthrough vessel 701 to and across clot 702 as shown in FIG. 15b . Device700 is then advanced through the microcatheter and deployed within theclot by retracting the microcatheter to a position proximal of theexpandable portion of the device as shown in FIG. 15c . The device andclot can now be retracted together and removed from the patient, or ifdesired, the user may elect to detach the outer expandable member fromthe rest of the device at this point. The detachment process is aspreviously described in relation to FIG. 14b , and results in the outerexpandable member apposing the vessel wall and/or clot as shown in FIG.15d , at which point the remainder of the device is retracted andremoved from the patient.

FIG. 16 shows one embodiment of a detachable proximal joint of a deviceof this invention, such as might be employed with devices 650 or 700previously described. Proximal strut 756 of the inner expandable memberterminates proximally in half collar 757 which is connected (soldered,bonded, welded or other means) to the distal end of shaft 750. Proximalstruts 752 and 753 of the outer expandable member terminate proximallyin half collars 754 and 755 which sit over the distal end of shaft 750and are prevented from separating outwardly by pull-wire collar 703, andfrom slipping distally by the shaft distal step 751. Pull-wire 758terminates in a pull-wire collar 760 and extends proximally to a pointadjacent the proximal end of elongate shaft 750 outside of the patient.Retraction of the pull-wire relative to the shaft retracts the pull-wirecollar which allows the half collars 754 and 755 to detach and separate,thus releasing the outer expandable member. In another embodiment thehalf collar 757 is a full collar and takes the place of step 751 informing a distal abutment surface against which the split collars 754and 755 of the outer expandable member lie.

FIG. 17a shows a side view of device 800, which is an expandable clotretrieval device configured to self expand to a shape that occupies atleast two planes. In the embodiment shown shaft 801 is connected to anexpandable body which comprises a proximal section 802, a middle section804, and a distal net section 805. The middle section 804 comprises agenerally cylindrical body including cells 806 from which protrude clotengaging petals 803. The entire expandable body may be formed from amonolithic structure of struts and connectors, and the distal net may beformed from the same structure or may incorporate fibres or wires or amembrane to reduce the pore size of its openings and increase itsscaffolding density. Proximal section 802 may be configured with anexpanded diameter smaller than that of the body of middle section 804.Petals 803 may be configured to expand outward to a larger diameter thanthat of the middle body section.

FIG. 17b shows a detail view of a portion of the cut pattern of themiddle section 804 as it looks prior to expansion. Petals 803 fit withincells 808 and are connected to the cell and body proximally atconnectors 808, and are unconnected at distal crowns 807. This designenables a single piece of tubing to be used to manufacture a threedimensional device which can occupy multiple planes when expanded. Thusmany of the features and benefits of the dual layer inner and outerexpandable member designs described elsewhere can be incorporated in aone piece part. In one embodiment the proximal section 801 and middlebody section 804 have the same diameter and function in a similar mannerto the inner expandable member described previously, creating a flowchannel through the clot and reducing the pressure gradient across theclot, without gripping or exerting any significant force on the vesselwall; while petals 803 engage with and grip the clot to retain itsecurely for retraction.

FIG. 18 shows the distal end of an inner expandable member similar topart 3 of device 1. This member comprises a framework of struts 854 andconnectors 855 forming a proximal body section 853, to which isconnected one or more elongate struts 852 configured in a spiral shapeand terminating in distal collar 851. This design creates a verycompliant spring to accommodate relative movement between this innerexpandable member and an outer expandable member or other part to whichit might be connected without exerting a strong axial force on the bodysection 853 which might tend to collapse or reduce its diameter. Thepitch, number of struts and number of turns of the spiral section 852may be varied to alter the compliance and the foreshortening of thissection. The diameter of this spiral section might in some embodimentsdiffer from that of the body section 853. In one particular embodimentthe spiral section diameter is greater than that of the body section 853and is similar to that of the outer expandable member. This embodimentcould be used in a similar manner to that described for parts 500 and606, and function as fragment protection filter.

FIG. 19 shows a clot retrieval device 877 partially restrained within aloading tool 875. The Loading Tool 875 comprises a generally tubularbody composed of a first material 880 and a second material 876. In theembodiment shown the first material is transparent and the secondmaterial is coloured and/or opaque and configured in a spiral stripearound or through the first material. This loading tool can be used tocollapse a clot retrieval device or to hold a clot retrieval device in acollapsed state prior to insertion into a microcatheter for delivery toa target location within a patient. The tool can also be used to reloada clot retrieval device for a second use if necessary to remove astubborn clot, in which case it is advantageous that the tool be easilyidentifiable, as it may have been dropped onto a sterile table or drapealong with numerous other items. The distinctive spiral pattern can bequickly identified even by a stressed and hurried user. It is alsoadvantageous that the first material 880 be transparent or at leasttranslucent so that the position of the clot retrieval device can beidentified through the wall of the tool. This is particularly helpfulwhen advancing the device from the loading tool into a microcatheter. Itis of of further advantage if the outer surface of the tube is of arelatively high coefficient of friction material and the inner surfaceis of a relatively low coefficient of friction material. The highcoefficient of friction outer surface means the tool can be easilygripped by the user and by a rotating haemostasis valve while in use,and the low coefficient of friction inner surface facilitates easyadvancement of the clot retrieval device through the tool. This can beachieved by using extruding the base tube from a low coefficient offriction material such as PTFE, and then roughening the surface (byetching or grit blasting or grinding or other such means) or by addingan outer sleeve of a higher friction material such as PET or Polyolefinfor example. Preferably this sleeve or roughening is not applied to thedistal few centimetres of the tool, to avoiding impacting on itstransparency.

FIG. 20 shows a portion of the body section of an inner expandablemember somewhat similar to part 3 of device 1. This body sectioncomprises a series of ring elements 901 connected to one another byconnector elements 902, forming closed cells 908. Each cell has aproximal apex 900 and a distal apex 907. Each ring element is offsetfrom each neighbouring ring element such that the apices 900 and 907 areoffset from each other relative to the central axis of the member. Thisoffset provides for greater bending flexibility in the member because inaddition to flexing of the struts forming each cell, the connectorsthemselves can flex to accommodate a bend in this offset design. Line905 is an axis through the proximal apex of cell 908 parallel to theaxis of the member. Line 904 is an axis through the distal apex of cell908 parallel to the axis of the member. Thus the perpendicular distancebetween lines 904 and 905 represents the offset between adjacent ringelements. Lines 909 and 910 are lines through the proximal and distalends of connector 902, perpendicular to the central axis of theexpandable member. Thus the perpendicular distance between lines 909 and910 represents the axial spacing between the ring elements. In oneembodiment the distance between lines 904 and 905 is less than thatbetween lines 909 and 910. In another embodiment the distance betweenlines 904 and 905 is equal to that between lines 909 and 910. In oneembodiment the distance between lines 904 and 905 is greater than thatbetween lines 909 and 910. In general it is desirable to maximise theoffset and minimize the spacing in order to achieve an optimal balancebetween clot scaffolding and device flexibility.

FIGS. 21a and 21b show an alternative embodiment of an outer expandablemember such as part 2 of FIG. 1. FIG. 21a illustrates a side view of theouter member and FIG. 21b shows the barrel section of the outer memberunrolled into a 2D configuration. In this embodiment the proximal collar970 is connected to proximal struts which in turn are connected to aseries of struts that form cells along the body section of the device.These cells are configured to act as large inlet windows 973, 978, 979,983, 984, 985, or smaller highly scaffolded cells 972, 977, 980, 981,982. The large inlet window cells facilitate movement of the clot intothe outer member and into the reception space between the outer memberand inner tubular member. The smaller highly scaffolded cells engagewith the clot and help dislodge the clot from the vessel. They alsopromote the movement of the clot from the highly scaffolded areas intothe inlet windows of the device.

The distribution of the large inlet windows and smaller cells is key tothe performance of the device and in this configuration the large inletwindows and smaller scaffolded cells are generally alternated along thelength of the device, for example large cell 973 is adjacent to smallercell 977 which is adjacent to larger cell 978 which is adjacent tosmaller cell 980, along the length of the device. In this configurationthe larger inlet windows and pairs of smaller scaffolded cells are alsogenerally alternated radially around the circumference of the device.For example large inlet window 978 is adjacent to smaller cells 981 and982 which are adjacent to large inlet window 983 around thecircumference of the outer member.

In this embodiment the proximal struts 971 are connected to a ring ofsmaller scaffolded cells 972 around the proximal end of the outermember. The distal end of the body section may be connected to a ring ofstruts 974 that provide sufficient radial force to prevent the movementof clot past the distal end of the device during retraction in thevessel. The distal ring of struts 974 is connected to a series of struts975 which form a closed end on the outer member and terminate at thedistal collar 976.

It will be apparent from the foregoing description that, whileparticular embodiments of the present invention have been illustratedand described, various modifications can be made without departing fromthe spirit and scope of the invention. Accordingly, it is not intendedthat the present invention be limited and should be defined only inaccordance with the appended claims and their equivalents.

The invention claimed is:
 1. A clot retrieval device for removing clotfrom a blood vessel, the device having a collapsed deliveryconfiguration and an expanded deployed configuration and comprising: aframework of struts forming a tubular porous inner body flow channelwith a proximal portion and a distal portion; and a framework of strutsforming an outer tubular body having a proximal end located at oradjacent the distal portion of the porous inner body flow channel, theouter tubular body distally tapering from the proximal end and radiallysurrounding the distal portion of the porous inner body flow channelduring both the collapsed delivery configuration and the expandeddeployed configuration; a distal scaffolding zone comprising a pluralityof strut elements that form a generally conical tapering with a distalend of the outer tubular body, wherein strut elements of the scaffoldingzone comprise a pore size smaller than cells of the tubular porous innerbody; wherein the outer tubular body comprises a plurality of cells thatare larger than the cells of the porous inner body flow channel, theouter tubular body being expandable to a radial extent to define a clotreception space.
 2. The device of claim 1, wherein a porosity providedby the porous inner body is greater than a porosity provided by theouter tubular body.
 3. The device of claim 1, further comprising: anelongate member having a distal end coupled to a proximal end of theporous inner body at a connection point.
 4. The device of claim 3,wherein the connection point is radially offset relative to alongitudinal axis of the outer tubular body.
 5. The device of claim 1,wherein the outer tubular body further includes at least one clot inletmouth positioned between adjacent struts that form of at least one ofthe cells of the outer tubular body.
 6. The device of claim 1, whereinthe clot reception space is eccentrically arranged about a longitudinalaxis of the outer tubular body.
 7. A clot retrieval device for removingclot from a blood vessel, the device having a collapsed deliveryconfiguration and an expanded deployed configuration comprising: aframework of struts forming an inner body having a tubular main bodyportion in an expanded configuration, the inner body comprising aproximal portion and a distal portion; a framework of struts forming anouter tubular body having a proximal end located at or adjacent thedistal portion of the inner body, the outer tubular body distallytapering from the proximal end and radially surrounding the distalportion of the inner body during both the collapsed deliveryconfiguration and the expanded deployed configuration, a distalscaffolding zone comprising a plurality of strut elements that form agenerally conical tapering with a distal end of the outer tubular body,wherein strut elements of the scaffolding zone comprise a pore sizesmaller than cells of the inner body; and wherein the outer tubular bodycomprises a plurality of cells that are larger than the cells of theinner body; wherein a diameter of the tubular main body portion in theexpanded deployed configuration is less than 50% of a diameter of theouter tubular body in the expanded deployed configuration along alongitudinally-extending clot reception space between the main bodyportion of the inner body and the outer tubular body.
 8. The device ofclaim 7, wherein a porosity provided by the inner body is greater than aporosity provided by the outer tubular body.
 9. The device of claim 7,further comprising: an elongate member having a distal end coupled to aproximal end of the inner body at a connection point.
 10. The device ofclaim 9, wherein the connection point is radially offset relative to alongitudinal axis of the outer tubular body.
 11. The device of claim 7,wherein the outer tubular body further includes at least one clot inletmouth positioned between adjacent struts that form of at least one ofthe cells of the outer tubular body.
 12. The device of claim 7, whereinthe clot reception space is eccentrically arranged about a longitudinalaxis of the outer tubular body.
 13. The device of claim 7, wherein strutelements of the distal scaffolding zone are connected to the inner body.14. The device of claim 7, wherein the distal scaffolding zone forms afragment capture zone.
 15. The device of claim 7, wherein the inner bodyand the outer tubular body each comprise a mesh-like structure thecomprise the cells of the inner body and the outer tubular body.